As illustrated in FIG. 1, a brake system of a vehicle includes a hat part (referred to as a hub) 10 connected to an axle, a brake disc 20 connected to the hat part 10, brake pads (also referred to as a lining) 30 located at a position adjacent to frictional surfaces 21 of the brake disc 20 to selectively press the frictional surfaces 21 of the brake disc 20. The hat part 10 is connected to the axle through a connection means (not shown), and the brake disc 20 and the hat part 10 are connected to each other through a connection means 40.
As for the brake system, when the brake pads 30 press the frictional surfaces 21 of the brake disc 20, by slowing or stopping rotation of the brake disc 20 due to frictional force caused by friction between the frictional surfaces 21 of the brake disc 20 and the brake pads 30, a speed of a vehicle equipped with the brake system is reduced, or the vehicle equipped with the brake system is stopped.
In recent years, many expressways have been constructed, and thus drivers experience more high-speed driving. In addition, as the number of components of the vehicle required for driver's convenience and safety is increased, a weight of the vehicle is continuously increased. In order to stop a heavy-weight vehicle driving at a high speed, the brake disc 20 and the brake pads 30 having high level of braking ability are needed.
To achieve this, the brake disk 20 and the brake pads 30 are recently manufactured using carbon-fiber-reinforced ceramic composites having thermal impact resistance and wear resistance.
The carbon-fiber-reinforced ceramic composites are carbon-fiber-reinforced materials using ceramic matrixes. Hereinafter, the brake disc 20 that is manufactured using carbon-fiber-reinforced ceramic composites is referred to as a carbon-ceramic brake disc 20.
In the brake system, when the brake pads 30 press the frictional surfaces 21 of the brake disc 20 to generate braking force in the brake disc 20, high-temperature frictional heat is generated in the brake disc 20 and the brake pads 30. When the high-temperature heat generated in the brake disc 20 is not smoothly dissipated to the outside, the brake disc 20 or the hat part 10 may be distorted (deformed) due to a difference between thermal expansion coefficients of the hat part 10 connected to the brake disc 20 and the brake disc 20.
As a method of dissipating the heat generated in the brake disc 20 to the outside, a plurality of heat dissipation holes 22 is formed in the frictional surfaces 21 of the brake disc 20. The heat dissipation holes 22 penetrate the frictional surfaces 21 at both sides of the brake disc 20 to be perpendicular to the frictional surface 21.
Unfortunately, since the plurality of heat dissipation holes formed in the frictional surface 21 of the brake disc 20 has a small contact area with the outside and the heat is not smoothly transferred, it is difficult to effectively dissipate the heat generated in the brake disc 20 to the outside.